Objectives: To determine if prolactin levels are associated with glucose-insulin homeostasis in antipsychotic-treated patients with schizophrenia.
Method: Prolactin levels and glucose homeostasis (quantified using oral glucose tolerance testing, insulin measurement, and homeostasis model assessment) were measured in 15 patients with elevated prolactin levels secondary to antipsychotic treatment of schizophrenia (mean age, 30.4 years; SD, 5.3 years). The effect of reducing prolactin levels by switching patients' antipsychotic treatment to clozapine was ascertained by performing the measures before and after the switch to clozapine.
Results: There was no significant correlation between prolactin and glucose-insulin measures at baseline. There was a large reduction in prolactin (593 mIU/L) after switching to clozapine, but this was not associated with changes in glucose-insulin measures.
Conclusions: Prolactin is not a significant determinant of glucose-insulin homeostasis in patients taking antipsychotics for schizophrenia. There was no benefit from lowering prolactin levels using clozapine. This could be because prolactin does not have a major effect on glucose homeostasis or that the effects of prolactin reduction are countered by clozapine.